Visual representations of various real and schematic elements are extremely important to several technical fields as well as to the world of art. Architecture, for example, substantially involves the transposition of a mental image of a building's shape to the actual construction of the building. Similarly, electronic circuit design involves the usage of conventional drawing techniques to reflect images which are representational of actual components. In each of these circumstances, as well as others, it is extremely valuable to have a means to reproduce the visual images prepared in one aspect of a project for transposition into another aspect. It is also frequently valuable to have the drawings be readily modifiable under such conditions.
One area in which great strides forward have been recently made is that of computer aided design ("CAD") technology. In this field, digital and analog instruments are utilized for aiding in the transposition, modification, and creation of drawings and other visual images. This industry has been growing at an extremely rapid rate and appears to be destined to be the primary medium for future design of architectural items, electronic circuitry and the like.
The transposition of visual images into the computer medium and then back from the computer memory to a physical representation, whether it be on the surface of a visual monitor or on an actual physical print-out such as that created by a plotter, it is a very important aspect of the procedure. Speed and accuracy in achieving this sort of transposition is extremely important for successful results.
Traditionally, the transposition of an image from one physical medium to another took place by way of various mechanical tracing device. A typical draftsperson's equipment includes mechanical tracing machinery adapted for following lines and segments on a reference image and creating a copy of all or part thereof on a separate image. Various modifications of the equipment have been made in order to change the scale, modify the contrast and otherwise alter the original image in some way prior to completion of the object image. A good example of this genre is shown and described in U.S. Pat. No. 4,441,020, issued to T. Sakamoto, et al as the mechanical portion of the device. However, these sort of device tend to require constant effort on the part of the user which can be very painstaking and tedious.
Accordingly, it is desirable to minimize the effort required by the individual and the automate the process as much as is possible. A number of efforts have been made to electronically accomplish various aspects of the procedure. This permits the user to concentrate on the creative and detail aspects of the process rather than to be involved in mere replication. Some examples of attempts made in this area are included in U.S. Pat. No. 4,160,199, issued to F. Bardwell and U.S. Pat. No. 4,475,130, issued to A. Miller, et al. Another procedure for accomplishing similar results is described and shown in U.S Pat. No. 4,375,654 issued to J. Evans, et al. Each of these patents describes techniques utilized for the image transfer process.
An example of a pattern tracing system embodying optical technology, rather than purely mechanical, is shown in U.S. Pat. No. 4,486,654, issued to F. Brouwer. This is appropriate for tracing an image without intermediate modification.
One aspect of the process which is best adapted for accomplishment without constant human intervention is the technique of following or tracing line segments as subsets of the overall image. The teaching of the Bardwell patent is particularly adapted for efforts in this area. In its simplest form, this procedure involves operating upon a selected small component of an overall image in the nature of a non-intersected line segment. The object is to follow the selected segment on the original image and to accurately reproduce that segment on a separate object. This sort of procedure is repeated over and over again, with additional procedures utilized to handle portions of the image not separable into non-intersecting segments (such as solids and crossed lines) until the entire overall reference image has been reproduced.
One traditional technique utilized to follow line segments has been the technique known as "thinning" or "stripping". In this methodology, the reference segment is reduced by various procedures to have a single unit thickness, as defined by the apparatus. This unit thickness may be in the nature of pixel, as in visual data bit representations, or some other unit of measurement. Once the selected line segment has been reduced to a single unit width, then it may be followed as it curves or otherwise changes directions throughout its length. This technique has been used extremely widely and is represented by the disclosure of the Evans, et al patent. One disadvantage of this technique is that line width data is lost in the transition. That is, line segments on the reference image having different thicknesses will nonetheless appear in the object image as having the same thickness.
It is always desirable to improve on prior techniques in any area. In the line following or line tracking field, it is particularly desirable to obtain object images which are as accurate a reproduction of the reference image as possible. It is also desirable to accomplish these goals as quickly as possible and with a minimum of expense in the way of mechanisms and auxiliary equipment. Minimizing operator intervention is also a desirable goal.